Facility and method for cold rolling metal strip

ABSTRACT

In a facility for cold rolling a metal strip in a circulating oil-feeding system by jetting a low concentration coolant, in a neighborhood of an inlet side of a work roll and jetting a high concentration coolant at an upstream side of the jetting position of the low concentration coolant to conduct rolling, the metal strip is cold rolled with the cold rolling facility provided with a control equipment for varying a jetting amount of the low concentration coolant in accordance with a rolling rate so that a tip of a liquid pool of the low concentration coolant formed on a surface of a steel sheet at an inlet side of the work roll does not reach a jetting position of the high concentration coolant, whereby the rolling can be performed without losing a plate-out property even if the rolling rate is decreased.

CROSS REFERENCE TO RELATED APPLICATIONS

This is the U.S. National Phase application of PCT/JP2017/015523, filed Apr. 18, 2017, which claims priority to Japanese Patent Application No. 2016-084993, filed Apr. 21, 2016, the disclosures of these applications being incorporated herein by reference in their entireties for all purposes.

FIELD OF THE INVENTION

This invention relates to a facility and a method for cold rolling a metal strip and, more particularly, to a facility for cold rolling a metal strip by using a circulating system for supplying a lubricant and a method for cold rolling by using such a facility. Hereinafter, the invention is explained by taking a “steel sheet” as an example for the metal strip.

BACKGROUND OF THE INVENTION

Facilities for cold rolling a metal strip are divided, based on a system of feeding a lubricant (rolling oil), into a direct oil-feeding system wherein the rolling oil is directly jetted and fed onto a surface of a steel sheet and at the same time a cooling water is jetted onto a surface of a roll to cool thereof, and a circulating oil-feeding system wherein a cooling water (coolant) containing an emulsified rolling oil is fed to surfaces of a steel sheet and a work roll to simultaneously perform lubrication and cooling of the work roll. Since the rolling oil can be circulatingly used in the latter circulating oil-feeding system, the cost of the rolling oil is low as compared with the direct oil-feeding system using the rolling oil only once, while since the concentration of the rolling oil is low, the rolling property tends to be deteriorated.

In order to solve the above problem inherent to the circulating oil-feeding system, it is effective to increase the concentration of the rolling oil contained in the coolant. When the concentration of the rolling oil is increased, the lubricity between the metal strip and the work roll is improved, while the cooling power is decreased. Therefore, the concentration of the rolling oil in the coolant is usually controlled to about 2-4 mass %.

Even in the cold rolling facility of the circulating oil-feeding system, it is sometimes necessary to roll such a type of steel that has a large deformation resistance in a good productivity. As a technique meeting such a requirement is disclosed a “hybrid rolling” in Patent Literature 1. The hybrid rolling is a technique of jetting a coolant having a concentration of the rolling oil of about 2-4 mass % (hereinafter referred to as “a low concentration coolant”) at an inlet side of the work roll and jetting a coolant having a high concentration of the rolling oil of about 10-15 mass % (hereinafter referred to as “a high concentration coolant”) at an upstream side of the jetting position of the low concentration coolant. When this technique is adopted, a large amount of oil content can be adhered to the steel sheet surface by the feed of the high concentration coolant (hereinafter referred to as “plate-out”), so that the lubricity between the steel strip and the work roll can be increased to decrease a rolling load. Since a certain amount of time is necessary for the adhesion of the oil content to the sheet surface, in order to enhance the plate-out property, it is desirable to jet the high concentration coolant at a position separated from the work roll at a certain distance at an upstream side thereof.

PATENT LITERATURE

Patent Literature 1: JP-A-2007-144514 (Japanese Patent No. 4905056)

SUMMARY OF THE INVENTION

In an actual hybrid rolling, there is a case that a decrease of the rolling rate cannot be avoided due to defects or the like existing in a rolling raw material (base material). When the feeding amount of the low concentration coolant is made constant irrespectively of the rolling rate, if the decrease of the rolling rate is caused, a liquid pool of the low concentration coolant formed on the steel sheet surface at an inlet side of the work roll is expanded toward the upstream side to make the length of the liquid pool long, and hence a tip portion of the liquid pool at the upstream side may reach the jetting position of the high concentration coolant. At such a state, the high concentration coolant is jetted toward the low concentration coolant accumulated on the sheet surface, so that the high concentration coolant is mixed with the low concentration coolant and diluted, and hence the oil content in the high concentration coolant cannot reach the sheet surface, and the effect by the hybrid rolling cannot be obtained.

With regard to the above problem, it can be considered to further increase the concentration of the rolling oil in the high concentration coolant, but there is a problem that the amount of the rolling oil used is increased to deteriorate unit consumption.

It is also considered to move the jetting position of the high concentration coolant to an upstream side further separated from a zone forming the liquid pool of the low concentration coolant, but it is actually difficult because there is a restriction on the distance between stands in a cold rolling facility of tandem type or the like.

Aspects of the invention are made in view of the above problems inherent to the conventional technique, and an object thereof is to provide a facility for cold rolling a metal strip which is capable of rolling without damaging the plate-out property even if the rolling rate is decreased in a hybrid rolling of a circulating system and to propose a method for cold rolling a metal strip by using such a cold rolling facility.

The inventors have made various studies to solve the above task. As a result, they have found out that it is effective to provide the cold rolling facility with a function of varying the jetting amount of the low concentration coolant in accordance with the rolling rate and perform rolling while controlling the jetting amount of the low concentration coolant so that the tip of the liquid pool of the low concentration coolant formed on the sheet surface at an inlet side of the work roll does not reach the jetting position of the high concentration coolant, and aspects of the invention have been accomplished.

That is, one aspect of the invention is a facility for cold rolling a metal strip in a circulating oil-feeding system by jetting a low concentration coolant in a neighborhood of an inlet side of a work roll and jetting a high concentration coolant at an upstream side of a jetting position of the low concentration coolant to conduct rolling, characterized in that the facility is provided with a control equipment for varying a jetting amount of the low concentration coolant in accordance with a rolling rate so that a tip of a liquid pool of the low concentration coolant formed on a sheet surface at an inlet side of the work roll does not reach a jetting position of the high concentration coolant.

The facility for cold rolling a metal strip according to aspects of the invention is characterized by having a control equipment for varying a jetting amount of the high concentration coolant in accordance with the rolling rate.

The facility for cold rolling a metal strip according to aspects of the invention is characterized in that a concentration of a rolling oil in the low concentration coolant is 2-4 mass % and a concentration of a rolling oil in the high concentration coolant is 10-15 mass %.

Further, another aspect of the invention is a method for cold rolling a metal strip in a cold rolling facility of a circulating oil-feeding system by jetting a low concentration coolant in a neighborhood of an inlet side of a work roll and jetting a high concentration coolant at an upstream side of a jetting position of the low concentration coolant to conduct rolling, characterized in that a jetting amount of the low concentration coolant is varied in accordance with a rolling rate so that a tip of a liquid pool of the low concentration coolant formed on a sheet surface at an inlet side of the work roll does not reach a jetting position of the high concentration coolant.

The method for cold rolling a metal strip according to aspects of the invention is characterized in that a jetting amount of the high concentration coolant is varied in accordance with the rolling rate.

The method for cold rolling a metal strip according to aspects of the invention is characterized in that a concentration of a rolling oil in the low concentration coolant is 2-4 mass % and a concentration of a rolling oil in the high concentration coolant is 10-15 mass %.

According to aspects of the invention, the tip of the liquid pool of the low concentration coolant formed on the sheet surface at an inlet side of the work roll is controlled so as not to reach the jetting position of the high concentration coolant, so that it is possible to sufficiently obtain an effect by the hybrid rolling.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view illustrating a feeding system of a rolling oil in a conventional hybrid rolling.

FIG. 2 is a schematic view showing a relation between a rolling rate V and a length X of a liquid pool.

FIG. 3 is a view illustrating a state that a tip of a liquid pool reaches a jetting position of a high concentration coolant when a rolling rate is low.

FIG. 4 is a schematic view showing a relation between a jetting amount Q of a low concentration coolant and a length X of a liquid pool.

FIG. 5 is a view illustrating an example of a feeding system of a rolling oil in a cold rolling facility according to aspects of the invention for controlling a jetting amount of a low concentration coolant in accordance with a rolling rate.

FIG. 6 is a view illustrating a method of controlling a jetting amount of a low concentration coolant in the method for cold rolling according to aspects of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 1 is a view illustrating a feeding system of a coolant when a hybrid rolling technique is adopted in a conventional cold rolling facility of a circulating oil-feeding system. A steel sheet 1 is rolled by a work roll 2 to a predetermined sheet thickness. At this time, a low concentration coolant is jetted to a steel sheet surface from a spray header 3 by a spray pump 8 to enhance lubricity between the steel sheet 1 and the work roll 2 and conduct cooling of the work roll 2 simultaneously. The low concentration coolant used for jetting to the steel sheet surface is thereafter collected in a return tank 4 disposed in an oil cellar through an oil pan 11, returned to a clean tank 7 through a filter 6 disposed above ground by a return pump 5 and circulatingly used. In this case, the low concentration coolant jetted to the steel sheet surface from the spray header 3 forms a liquid pool 10 of a length X on the sheet surface toward an upstream side.

On the other hand, a high concentration coolant is prepared in a high concentration coolant tank 12 and jetted to the steel sheet surface from a spray header 9 by a spray pump 13. The high concentration coolant used for jetting is collected through the above oil pan 11, mixed with the low concentration coolant and circulatingly used as a low concentration coolant. Moreover, the spray header 9 for the high concentration coolant is disposed in a position located at an upstream side from the jetting position of the low concentration coolant and separated from the work roll at a distance of L toward an upstream side in order to sufficiently ensure a time required for the adhesion of oil content to the sheet surface to enhance a plate-out property. In this figure, numeral 14 represents a draining roll having a function of removing the coolant adhered to the steel sheet surface in the rolling at the previous stand.

FIG. 2 schematically illustrates a relation between a rolling rate V and a length X of a liquid pool of the low concentration coolant formed on the steel sheet surface at an inlet side of the work roll. Since the amount of the rolling oil drawn into a roll bite is varied in accordance with the rolling rate V, the length X of the liquid pool becomes long when the rolling rate is low and becomes short when the rolling rate is high.

FIG. 3 schematically illustrates a relation between the length X of the liquid pool of the low concentration coolant and a position of a spray header for the high concentration coolant disposed at a distance of L from the work roll toward an upstream side when the rolling rate is decreased. When the rolling rate V is low, the length X of the liquid pool of the low concentration coolant becomes longer than the distance L between the work roll 2 and the position of the spray header 9 disposed for the high concentration coolant and sometimes reaches to a position of the draining roll 14.

FIG. 4 schematically illustrates a relation between the jetting amount Q of the low concentration coolant and the length X of the liquid pool of the low concentration coolant. The length X of the liquid pool is varied in accordance with the jetting amount Q of the low concentration coolant. The length X of the liquid pool becomes shorter as the jetting amount Q becomes smaller, while the length X of the liquid pool becomes longer as the jetting amount Q becomes larger.

In accordance with aspects of the invention, therefore, when the rolling rate V is decreased, the length X of the liquid pool of the low concentration coolant is made shorter than the length L between the work roll 2 and the position of the spray header 9 disposed for the high concentration coolant by decreasing the jetting amount Q of the low concentration coolant. That is, the tip at the upstream side of the liquid pool is prevented from reaching the position of the spray header disposed for the high concentration coolant, whereby the high concentration coolant can be directly sprayed to the steel sheet surface all the time. In other words, aspects of the invention are characterized in that the jetting amount Q of the low concentration coolant is controlled in accordance with the rolling rate V to achieve cold rolling having an excellent plate-out property.

FIG. 5 illustrates an example of a coolant feeding system in the cold rolling facility according to aspects of the invention which controls the jetting amount of the low concentration coolant in accordance with a rolling rate. A flow regulating valve 17 is installed in the feeding system of the low concentration coolant. The jetting amount Q of the low concentration coolant is calculated by a distributed control system (DCS) 15 based on a command for the rolling rate from a driving motor 16 of the work roll so as to make the length X of the liquid pool of the low concentration coolant shorter than the distance L to the jetting position of the high concentration coolant, and the calculated result is given to the flow regulating valve 17 disposed in the feeding system of the low concentration coolant as an opening command.

Even if the rolling rate is decreased, when the high concentration coolant is jetted in the same amount as for a high rolling rate, the amount of the rolling oil jetted to the steel sheet surface becomes larger to increase the lubricity. However, when the lubricity becomes extremely high, an abnormal rolling such as slip or chattering is caused. Therefore, when the jetting amount of the high concentration coolant is adjusted in accordance with the rolling rate, a proper oil content required for the cold rolling can be fed, whereby the cold rolling can be stably performed.

In order to adjust the jetting amount of the high concentration coolant in accordance with the rolling rate, a flow regulating valve is disposed in the feeding system of the high concentration coolant similarly in the case of the low concentration coolant, whereby the jetting amount of the high concentration coolant may be adjusted within a proper range based on the command for the rolling rate.

In general, as the rolling rate becomes higher, a rolling load is increased, so that it is necessary to increase the jetting amount of the rolling oil fed. When the jetting amount of high concentration coolant is controlled in accordance with the rolling rate as above, it is possible to jet a proper amount of the rolling oil in accordance with the rolling rate.

EXAMPLE

FIG. 6 shows a relation between the jetting amount Q of a low concentration coolant and the length X of a liquid pool of the low concentration coolant formed on the sheet surface when the rolling rate is varied in three stages of 200 m/min, 400 m/min, and 1000 m/min.

In this figure, a point A shows the length X of the liquid pool when rolling is performed at a rolling rate V of 1000 mpm in a maximum jetting amount Q_(max) of the low concentration coolant. At the point A, since the rolling rate is high and a working heat generation amount per unit time is large, the work roll is cooled by jetting the low concentration coolant in a jetting amount of the maximum value Q_(max). However, since the amount of the low concentration coolant drawn into the roll bite is also large, the length X of the liquid pool is shorter than the distance L between the work roll and the position of the spray header disposed for the high concentration coolant.

When the rolling rate is decreased for some reasons such as defects in the rolling material, the length of the liquid pool is increased as shown in FIG. 2. For example, when the rolling rate V is decreased from 1000 mpm to 400 mpm, the length X of the liquid pool is transferred from the point A to a point B, and hence the length of the liquid pool becomes longer than the distance L between the work roll and the position of the spray header disposed for the high concentration coolant.

When the jetting amount of the low concentration coolant is decreased from Q_(max) to Q₁, the length X of the liquid pool is transferred to a point C and hence the length X of the liquid pool becomes shorter than the distance L between the work roll and the position of the spray header disposed for the high concentration coolant. In this case, cooling power of the roll is also decreased due to the decrease of the jetting amount of the low concentration coolant, but the working heat generation amount per unit time is also decreased by the decrease of the rolling rate, so that no problem is caused.

Further, even when the rolling rate V is further decreased from 400 mpm to 200 mpm for some reasons such as a division of the steel sheet into plural coils at an outlet side, the length X of the liquid pool is transferred from the point C to a point D by decreasing the jetting amount of the low concentration coolant to Q₂, so that the length X of the liquid pool becomes shorter than the distance L between the work roll and the position of the spray header disposed for the high concentration coolant.

DESCRIPTION OF REFERENCE SYMBOLS

1: metal strip (steel sheet)

2: work roll

3: spray header for low concentration coolant

4: return tank

5: return pump

6: filter

7: clean tank

8: spray pump

9: spray header for high concentration coolant

10: liquid pool of low concentration coolant

11: oil pan

12: tank for high concentration coolant

13: spray pump for high concentration coolant

14: draining roll

15: distributed control system

16: driving motor for work roll

17: flow regulating valve for low concentration coolant 

1. A facility for cold rolling a metal strip in a circulating oil-feeding system by jetting a low concentration coolant in a neighborhood of an inlet side of a work roll and jetting a high concentration coolant at an upstream side of a jetting position for the low concentration coolant to conduct rolling, characterized in that the facility is provided with a control equipment for varying a jetting amount of the low concentration coolant in accordance with a rolling rate so that a tip of a liquid pool of the low concentration coolant formed on a surface of a steel sheet at an inlet side of the work roll does not reach a jetting position of the high concentration coolant.
 2. The facility for cold rolling a metal strip according to claim 1, which is provided with a control equipment for varying a jetting amount of the high concentration coolant in accordance with the rolling rate.
 3. The facility for cold rolling a metal strip according to claim 1, wherein a concentration of a rolling oil in the low concentration coolant is 2-4 mass % and a concentration of a rolling oil in the high concentration coolant is 10-15 mass %.
 4. A method for cold rolling a metal strip with a cold rolling facility in a circulating oil-feeding system by jetting a low concentration coolant in a neighborhood of an inlet side of a work roll and jetting a high concentration coolant at an upstream side of a jetting position of the low concentration coolant to conduct rolling, characterized in that a jetting amount of the low concentration coolant is varied in accordance with a rolling rate so that a tip of a liquid pool of the low concentration coolant formed on a sheet surface at an inlet side of the work roll does not reach a jetting position of the high concentration coolant.
 5. The method for cold rolling a metal strip according to claim 4, wherein a jetting amount of the high concentration coolant is varied in accordance with the rolling rate.
 6. The method for cold rolling a metal strip according to claim 4, wherein a concentration of a rolling oil in the low concentration coolant is 2-4 mass % and a concentration of a rolling oil in the high concentration coolant is 10-15 mass %.
 7. The facility for cold rolling a metal strip according to claim 2, wherein a concentration of a rolling oil in the low concentration coolant is 2-4 mass % and a concentration of a rolling oil in the high concentration coolant is 10-15 mass %.
 8. The method for cold rolling a metal strip according to claim 5, wherein a concentration of a rolling oil in the low concentration coolant is 2-4 mass % and a concentration of a rolling oil in the high concentration coolant is 10-15 mass %. 